See the marginal references. If the number of warders was, as stated in Nehemiah (Nehemiah 11:19) 172 (i. e. 168 besides the four chief warders), and the number employed at any one time was, as under David 1 Chronicles 26:17-18, twenty-four, then the turn of the courses to keep ward came every seven weeks.
Related Commentaries of 1 Chronicles 9:25
1 Chronicles 9:25
25 And their brethren, which were in their villages, were to come after seven days from time to time with them.